The introduction of the first commercial termite bait system, SENTRICON®, in 1995 drastically changed the landscape of subterranean termite control practices. Traditional soil insecticide applications in the last half-century typically use 100-200 gallons (or 5-10 kg active ingredient) of pesticide to kill soil-borne subterranean termites in the immediate vicinity of the treated house. Because a subterranean termite colony may contain a gallery system that extends up to 300 feet from an infested house, soil treatments (despite the quantity of insecticide applied) seldom impact the entire colony. A monitoring-baiting program such as SENTRICON®, on the other hand, is capable of eliminating the entire colony. See WO 93/23998.
This type of system relies on periodic, routine monitoring. Stations containing monitoring devices are first placed in the soil to detect termites. When termites are found in a station, the monitoring device is replaced with baits containing a small amount of insecticide such as hexaflumuron. Termites are allowed to continue feeding on baits, which distributes the active ingredient throughout the colony population until the entire colony is eliminated. Because of the target-specific approach, only a few grams of hexaflumuron are needed to eliminate a colony that may contain several hundred thousand termites (Su 1994, J. Econ. Entomol. 87:389-397).
Due to its low environmental impact, hexaflumuron was the first compound to be registered under EPA's Reduced Risk Pesticide Initiative. The SENTRICON® system was the recipient of EPA's Presidential Green Chemistry Award in 2000.
Various other subterranean termite baiting systems, both proposed and commercial products, also employ the monitoring-baiting approach. U.S. Pat. No. 5,329,726 (Thorne et al.), for example, adopted a “diagnostic” phase before bait placement. Japanese Patent No. 63-151033 (System Maintenance, Inc.) describes a system in which a wooden housing containing another wooden detector was first placed in soil to attract termites, and the detector was replaced with an insecticide material when termites were found in the wooden housing. U.S. Pat. No. 5,950,356 (Nimocks & David) describes an apparatus comprising a housing, with an opening, that contains nontoxic baits to detect termites. Toxic baits are placed into the housing without removing the nontoxic baits when termites are detected in the housing. U.S. Pat. No. 5,937,571 (FMC Corp.) describes a tamper resistant bait station containing cellulose baits. The station has a plurality of apertures to allow termite access to a cellulose bait impregnated with a slow-acting toxicant. U.S. Pat. No. 4,043,073 relates to a rigid container that encloses bait material for termites or other pests, wherein the bait has an odiferous material in it to signal to humans when the container has been attacked by pests. U.S. Pat. No. 6,100,805 relates to a spike-shaped tube for termite detection. A conductive loop is present between two wooden blocks inside the tube.
Cellulose-based baits (for monitoring and/or toxicant delivery) degrade rapidly in the environment, as they are placed in soil and exposed to outdoor elements (rainfall, temperature fluctuation, high humidity, and biotic factors such as fungal decay and other insects). This necessitates frequent onsite inspection and replacement of these cellulose baits. These systems are intended for both remedial and preventative control, and rely on a routine monitoring program (primarily to detect termites so that toxic baits can be applied). The manual, onsite inspection currently required to maintain these systems is also the most labor-intensive and costly element of the systems. Moreover, the onsite monitoring procedure becomes virtually impractical when the system has to be used to protect, for example, an entire city or large agricultural areas. Protecting the entire city of New Orleans and/or Ellis Island would be examples. Subterranean termites are known to damage sugarcane, rubber trees, and oil palm trees, for example; thousands of stations are needed for effective control of termite populations in an agriculture plantation. Stations placed in the plantation tend to get lost in the vastness of the land, and inspection of such a large number of stations is not practical or cost-effective.
Another category of termite baiting methods is intended for remedial control, i.e., to be used after termites are found. As with many in-ground systems typically used in monitoring-baiting programs, baits for remedial control are applied only when termites are present. The prior art generally used either a rigid outer housing with openings to allow termite access to a toxicant, and/or an exposed, cellulose/wood block (with a toxicant). An above-ground station made of a re-closable plastic bag containing bait matrix was described by Su et al. (1997, J. Econ. Entomol. 90:809-817). This station has an opening to allow for termite access to the baits. This system was placed directly over active infestations of subterranean termites in a house or tree to allow for immediate bait consumption by termites. U.S. Pat. No. 5,778,596 (Henderson & Chen) describes an elaborate double-chamber baiting system that is placed in the vicinity of termite populations so that termites can be placed in the first chamber (containing non-toxic food) and thus preconditioned before entering the second chamber (that contains bait/toxic food). U.S. Pat. No. 6,058,646 (Bishoff et al.) relates to an above-ground system that employs a plurality of interchangeable station housings that contain termite baits. The housings have orifices that allow termites to have immediate access to the baits, and multiple stations can be stacked on top of each other while maintaining continuous termite access to the baits. These systems require a periodical inspection for bait replacement. Thus, with manual operation like the in-ground systems, costly onsite visits by technicians are unavoidable.
Typical bait housings currently in use provide openings for termite access to baits. No provisions are made to effectively protect the cellulose-based baits from the environmental elements such as rainfall, high humidity, temperature fluctuation, and other biotic factors (such as fungal decay often associated with wooden and other cellulose-containing bait materials). WO 93/23998 describes a bait casing, but that is primarily to facilitate easy handling of the bait.
Even with baiting-monitoring systems that use an easily removable bait to minimize disruption to foraging tunnels, another continuing problem is “station avoidance” by particularly “shy” termite species such as Reticulitermes virginicus in North America, or R. speratus in Asia. These species are known to be highly sensitive to disturbance and have a tendency to stay away from feeding sites that are disturbed in any way. For these species, the monitoring-baiting procedure can be less effective because once the stations are opened and baits are placed, termites often do not return (at least for an extended period) to the stations to consume the baits.